Multiplex synchronizing system



April l, w47. D. D. GRIEG MULTIPLEX SYNCHRONIZING SYSTEM 2 Sheets-Sheet1 Filed pec. 2o, 194s April 1 1.947- D. D. emes 2,418,116

MULTIPLEX SYNCHRONI Z ING SYSTEM Filed Dec. 20, 1943 2 Sheets-Sheet 2 LJ Ffa/w 3d Maz vv/amm@ 38 1N VEN TOR. 00A/HZ 0 0. GfP/EG ATMP/VFY-Patented pnl, 1947- y 4UNITED STATES PATENT. or-Fice MULTIPLEXSYNCHRONIZING SYSTEM Donald D. Grieg, Forest Hills, N. Y., assigner toFederal Telephone and Radio Corporation, New York, N. Y., a corporationof Delaware Application December 20, 1943, Serial No. 514,998

20 Claims. (Cl. 179-15) This invention relates to synchronizingsyshalted. The channels and receivers are so ar tems particularlyadapted to synchronize multiranged that when the Progression i8 haltedthe f plex pulse system channels to assure proper channels are eachproperly aligned with their alignment thereof. associated receiver.Multiplex communication systems have been The synchronizing system isadapted to line up proposed in which each channel comprises a train anymultiplex pulse system regardless of its'purof spaced impulses. Thepulses of each channel pose. It is contemplated for use more particuarespaced apart a predetermined distance and larly. however, incommunication Systems Where-- the pulses of each train are interleavedin such in the pulses are modulated with different sigspaces so that aplurality of separate messages 10 nals. These signals may be applied asamplimay be carried simultaneously on a common tude modulation of thepulses. orSoIne form medium. In such systems the Areceivers, are of timemodulation such as cadence frequency adapted to select a single channel,and some modulation, 0r time displacement modulation. or means must beprovided to assure a proper alignas pulse width modulation as desired.When ment of each channel with its associated receiver. cade-noefrequency modulation" of pulses is ein' This may be done by a visual oraural monitorployed the synchronizing signal must, of course, ingcircuit. Such monitoring, however, requires be chosen outside of thefrequency band of the that an operator manipulate some control toSignals transmitted over the other channels or effect the alignment. l pat least the frequency of the synchronizing signal It is an object' ofmy invention .to provide a` 20 must be excluded from the intelligenceSignals synchronizing system and method for a multiplex transmitted overthe channels.

pulse transmission system, which will assure A better understanding ofmy invention and proper automatic augnment of the lpulse chanthe objectsand features thereof may be had from nels with a, receiving system. theparticular description of an embodiment It is a further object of myinvention to provide thereof made With reference to the accompanyareceiver for receiving suitably modulated lng drawing, in Which:

pulses, and effecting a proper alignment of a plu- Fig. 1 is a schematicblock circuit diagraml of rality of pulse channels in response to themodua .multiplex transmission System` in accordance lation of thereceived pulses. with my invention;

According to aefeatureof my invention, I pro- 5'0 Fig 2 iS a Circuitdiagram of a time `displacevide, at the transmitting terminal of amultiplex ment modulator which may be used in the circuit pulse`communication system, a synchronizing of Flgl; 1 l source' which is usedto modulate the pulses of Fig. 3 is a circuit diagram of a Selector andone channel. At the receiving end is provided a channel detector whichmay be used in the circuit selecting oscillator circuit operating at afre- 0f Fig- 1;

quency or- Vcadence slightly lower than the Fig- 4 iS a modi-fied formof channel detector cadence frequency of the pulses of a channel. foruse in a circuit Suc h aS Shown in Fi8- 1; and The output wave from theselecting oscillator Fig.5isa.pulse diagram illustrating theoperacircuit serves to successively select pulses of the tion of asynchronizer in accordance with my inrespectiv'e channels atsuccessively dilerent re- 40 Vention.

ceivers. Thus, in lnormal operation, the selection In Fig- 1 isyillustrated dia81al. luni'ttioally a progressively applies successivelydifferent chanmultiplex channel system `to which the prinnels to eachreceiver. In the output of one re- Ciples of my invention have beenapplied- Inceiver circuit is provided a filter tuned to select comingsignals over lines l0. il. l2 and Il are the demodulated synchronizingsignal and apply lapplied over hybrid coils i4, i5, l5 and il to it tothe selecting oscillator circuitl to synchronize the respective channelmodulators I8, I9, 2l and this oscillator to the normal pulse cadencefre- 2|.` respectively. `In addition, energy from a quency. Thus ineiect this one receiver circuit synchronizing source 22 is applied t0channel successively tests theincoming channels to find modulator I8.l Acontrol wave source 23 prothe one having thereinthe synchronizingsignal. duces a switching control wave tosequentially Accordingly, when`the progressive application energize channel modulators L8 to 2|,Yrespecof channels reaches the point where the modutively, overindividualphase shifter units 24,' 2i, lated pulse series is appliedpto thlsonereceiver, 26 and 21. Each of the channel modulators Il the oscillator isbrought into synchronism and to 2|, inclusive, produces a series 'oi'pulses whichr the successive application to different receivers is aremodulated to carry the desired message in- `shifters 44, 45, 48 and 41may be 3 coming over their respective lines I8, il, I2 and I8. Thismodulation may be amplitude modulation, or some form of time modulationsuch as cadence frequency modulation, time displacement modulation orwidth modulation of the pulses. Through the operation of the controlwaves and the phase shifters, the pulsesfrom the respective channels areapplied to line 28 in such order that the pulses of the separatechannels are interleaved one with another.

'lhese pulses are then transmitted to the remote end of line 28 wherethey are applied to channel detectors 88, 3|, 32 and 33 over individualchannel selectors 34. 85, 38 and 81. At the receiving station isprovided a channel selector wave generator 88 which is preferably amultivibrator producing square wave impulses at a cadence frequencyslightly lower` than the cadence frequency of the pulses of a channel.'I'hese square wave pulses are applied to selector 34 and over delaycircuits 38, 48 and 4| to selectors 35, 88 and 81 so that incomingchannels are selectively applied to the channel detectors 38, 8|, 82y

and 88, respectively.

' Since the cadence frequency ofthe multivibrator pulses is slightlylower than the cadence of the pulses of the incoming channels, thechannels will be progressively applied to different channel detectors.This progression will continue until such time as channel is applied tothe corresponding detector 38 for channel I. At this time, in the'output of channel I, will be present the synchronizing voltage fromsource 22. 'I'his synchronizing voltage is picked oif in synchronizingwave filter 42 and applied to multivibrator 88 to synchronize itsoperation to the average pulse cadence frequency. As a consequence, Vtheincoming pulse channels will then b`e applied to the proper detectorcircuits without further .progression-and `all the channels will beproperly aligned. To operate the channel detectors a wave -source 43 maybe provided synchronized with the output of multivibrator 38 to producea demodulating wave. This demodulating wave may be applied to channeldetectors 38 to 88, respectively, over separate phase shifters 44, 45,48, and 41. The detected outputs of the separate channels may then beapplied over hybrid `coils 48, 49, 58 and 5| tothe corresponding audiofrequency output lines 52, 53, 54 and 55.

Since energy from synchronizing source 22 is continuously applied tochannel. I, a illter 58 is provided in the output of channel I toprevent application ci' this synchronizing source tothe audio frequencyline 52.

At the transmitting end of the line, receiver circuits may be coupled tothe hybrid coils I4, I5, I8 and |1 by means of lines 51, and at thereceiver transmitters may be coupled to hybrid coils 48, 43, 58 and 5|through lines 58.

Furthermore, at the receiver end of the line, individual demodulationcontrol for the detectors 88, 8| and 32 may be provided, if desired, inwhich case demodulating wave source 43 and phase eliminated. While onlyfour channels have been illustrated for the purpose of simplifying theshowing, itis clear that a much larger nu'mber of channels may bemultiplexed in accordance with my system.

'111e only limitation on the number of channels applicable to the linedepends on the width of the pulses used, the cadence frequency necessaryto carry the message and the amount of time displacement or widthvariation which may occur i n the modulation circuits.

i copending application,

In Fig. 2 is illustrated a channel modulator suitable for use in thesystem. as illustrated in Fig. 1. In this arrangement the signal inputmay be applied over a line 88 and a filter 8| serving to eliminate thesignal frequency corresponding to the frequencv of the synchronizingsource to a mixing circuit indicated generally at A18 simultaneouslywith synchronizing` signals incoming over line 82. Mixer`18 comprisestwo vacuum tubes 1| and 12 suitably biased, for example, by cathoderesistor bias means 13 and 14. The output circuit of these two tubes isconnected in parallel and the combined Waves are applied over a couplingcondenser 15 to the input or modulating coils 18 'of' a time modulationcircuit. The control wave from a source such as 23 is applied over line11 to coil 18 of the modulator. I'his control wa've,modulated with theotherinput waves, is applied over separate transformer connections 8l,8| to the grids of a -pair of rectifier tubes 82, 88. These tubes, asshown, are similarly biased so that in the absence of modulating inputthe rectiiled wave will be uniform providing equally spaced peaks orcusps. The modulating voltages serve to alter the effective bias of therectiers between the limits shown at 88 and 81 and thus vary thepositions of the peaks of wave 85 between limits on opposite sides ofthe unmodulated position, (e. g., as at curve 85) dependingupon themodulation. These output peaks are then applied over acoupling-condenser 88 to pulse shaper 83 which serve to` narrow thepulses and produce the desired shape for transmission of thecommunication line. .A more complete understanding of this type of timemodulating transmitter arrangement may be obtained from a reference toSerial No. 455,897, filed August 24, 1942. I t should be furtherunderstood that in the other channels where the synchronizing in'put isnot required; this portion of the 4circuit may be eliminated. Likewise,filters 8| synchronizing circuit at the receiver might apply a tonefrequency to the line equal to the synchron1 may not be necessary in allcases but are provided as a precautionary measure since without thesefilters anyone familiar with the operation of the nizing frequency whichwould serve to improperly align the receiving channels. In Fig. 3 isillustrated a circuit diagram of a 50 selector and channel indicatorarrangement which may be used in the system of Fig. 1 in conjunctionwith a transmitter arrangement, such as shown in Fig. 2. In thisarrangement, selector 84 is shown to comprise a mixing tube |88. Thistube preferably is of the double grid type in which the two grids are soarranged that the signals incoming on the separate grids tend to combineto increase the output of the tube circuit. The pulses |8| incoming overthe line are applied to one of the grids and the selector waves |82 frommultivibrator 38 are applied to the other grid. Tube |88 is biasedbeyond cutoif so that. Ain the absence of both signals being present atthe same time, no output is obtained from the tube. Selector pulses |82applied to their grid of tube |88 serve to Partly remove the bias sothat the tube is .lust below cut-olf. When signal pulses |8| are appliedwhile pulses |82 are present in the tube the combined pulses will appearas shown in the curve |88.

Because of the .bias on tube |88. this tube serves 'as a clipper at thesame time as it serves as a 'mixer and output pulses |84 are obtainedtherefrom. A rectifier |85 is coupled across the input |82 so that thesewaves will always reach a predetermined constant maximu'm voltage levelat the tube. It will thus be seen that the selector 34 serves to selectonly one train of pulses corresponding to a single channel.

In the demodulator circuit an alternating current wave |06 is appliedsimultaneously with the pulse train |04 to a mixingl tube ||0. Thefrequency of wave |06 is a harmonic of the control wave frequency,preferably, an even harmonic thereof. In tube then will be produced thecombined wave form |01. It is evident that the pulses |04 will be raisedto different levels above the clipping voltage of tube ||0, depending ontheir time position relative to detector wave |01. As a consequence, inthe output of tube H0 will be present a plurality of pulses having anenvelope frequency corresponding to the modulations of pulses i 0|. Thisoutput signal is then applied over a low-pass lter H which serves toremove the pulse cadence frequency, to line ||2 leading to thesynchronizing filter 42 and to filter 58 and hybrid coil 48. This sametype of detector arrangement may be provided for each of the channelsshown in Fig. 1. The control wave for the detector is shifted in phaseproperly to align it with the pulses of each of the selected channels.

In Fig. 4 is illustrated a modied form of receiver circuit eliminatingthe necessity of a separate control wave source, as is used inconnection with the circuit of Fig. 3. In this arrangement, the selectedpulses from channel selector 34 are applied to the detector tube |20.These pulses serve to excite a tuned tank circuit |2| at the averagecadence frequency of the applied pulses. Thus, a detecting wave isgenerated directly in circuit |2| which combines with the incomingpulses to Provide output pulses having a variable amplitude envelope ina manner similar in operation to the combining circuit described inconnection with Fig. 3. This receiver circuit is of the type fdescribedmore fully in my copending application Serial No; 459,959, filedSeptember 28, 1942. The output pulses from |20 may be applied overlow-pass filter to filter 56 and to line ||2 leading to thesynchronizing filter arrangement.

In order more fully to explain the operation of the channelsynchronizing system, reference may be had to Fig. 5. Curve' A of thisgure illustrates the pulse responding channels to 4, inclusive. In curveB is shown the combination of pulses from the multivibrator selectorarrangement and the incoming channel pulses. As illustrated in thecurves, the channels first arrive at the receiving end in such positionthat channel 3 is initially selected. However, because the cadencelfrequency of the square wave pulses for multivibrator 38 issomewhatlower than the cadence frequencyof the channel pulses, the selectionprogressesffrom channel 3 to channel 4 and from channel 4 to channel l.Once channel I is selected, the synchronizing wave is able to e'ectcontrol of the multivibrator circuit 38 and pull it into` step so thatchannel [continues to be selected at fthis point. The other selectorWaves, because of the delay circuits are also then properly timed toselect a single channel and apply it to the respective channelindicators.

For purposes of illustration; the .cadence lfrequencyis shown toprogress by half of the pulse interval of the combined pulse trains, itshould upon reaching' channell, sufdc'ient number ofV pulses will bedetected during the period of transversal of the selector pulse toconveythe synchronizing frequency to the multivibrator. It should further beunderstood that While the progression is relatively slow, the cadencefrequencies for each channel are above normal audio frequencies, forexample, in the range of 12 kilocycles or the like. Accordingly severalhundred pulses may be selected from each channel without consuming anappreciable amount of time in bringing the circuit into propersynchronism.

While in the principal example given the selector system is shown usedto align a plurality of multiplex channels it is clear that theprinciples of my invention may be applied for the purpose of causingselective operation of any one receiver to pick out a, desired channel.For this purpose individual selector wave generators may be used witheach receiver circuit as shown in connection with channel one.Individual selector wave generators, with synchronizing wave lters maybe provided to pull the selectors into step with a channel to which theparticular synchronizing frequency has been applied. Thus any channelmay be selected by simply modulating it with the proper synchronizingwave.

This principle may also be used for selectively dropping or interceptingat an intermediate point in the line any desired channel or channels.

With a description of a speciilc embodiment and modifications thereof asgiven herein, it is clear that one skilled in the art may develop manyother circuits and arrangements to accomplish the result in accordancewith my invention. The specific example is intended merely as anillustration and not as a limitation on the scope of my invention, asset forth in the objects of the invention and the accompanying claims.

What is claimed is:

l. In a communication system having a iirst terminal means fortransmitting a plurality of trains of vpulses of a given average cadenceeach train representing a channel of communication, means for timingsaid separate trains of pulses in a given time displacement so that thepulses of successive trains are interleaved with respect to one another,and means for imparting to the cation to said receiver means, a selectorwave generator operating at a cadence lower than said given averagecadence, tosupply aiselector wave to said selector means, whereby itwill serve to selectprogressively dilerent channels for said receivermeans, filter means coupled to the output of said receiver means forselecting` said modulation of said predetermined!` .frel-A `quency, andmeans for applying said selected modulations to saidselectonwave,generator to synchronize its operation with said givenaverage cadence, whereby said one channel 'will be: con= tinuouslyapplied to said receiver` means.

munication, means for timing said separateetrains of pulses in a given.timef displacement so that the pulses of successive trains areinterleaved with respect to one another,`fand means for ini#parting-tothe pulses ofonefof said" channels a modulation of apredetermined frequency; and a second terminal including individualreceiver means for said trains of pulses, separate selector means eachfor selecting a single channel for application to corresponding receivermeans, a selector wave generator operating at a cadence lower than saidgiven average cadence to supply a selector wave to each selectormeans,whereby it will serve to select progressively different channels forrespective ones of said receiver means, lter means coupled to the outputof the receiver means for said vone channel for selecting saidmodulation of said predetermined frequency, and means for applying saidselected modulations to said selector wave generator to synchronize itsoperation with said given average cadence, whereby said channels will becontinuously applied to their corresponding receiver means.

3. A multiplex system according to claim 2, further comprising means forsignal modulating the pulses in each of said trains, means fortranslating the signal output from each of Said receiver means, andmeans in the output of said one receiver between said translating meansand said filter means for eliminating said selected modulations fromsaid translator device.

4. A multiplex sy'stem according to claim 2, further comprising aplurality of sources of signals, a plurality of pulse generators, meansfor coupling said sources to said pulse generators to signal modulatesaid pulses, filter means in said coupling means to block signalfrequencies of said predetermined frequency present at saidsignaflsources from signal modulatingsaid pulses.

5. In a multiplex system in which separate dence, whereby it will serveto select progressively different channels for respective ones of saidselectors, said selector wave generator kserving to producesubstantially rectangular pulses having a width less than said givenaverage spacing to supply a selector Wave to each selector,l filtermeans coupled to the output of the selector for said one channel forselecting said modulation of said predetermined frequency, and means forapplying said selected modulation to said selector wave generator tosynchronize its operation with said given average cadence, whereby saidchannels will be continuously applied `to their corresponding selectors.A

1, A multiplex system according to claim 6, further comprising meansjfor signal modulating the pulses in each of said trains, means at saidsecond terminal for detecting signal output from each of said selectors,and further filter means in the output of the detecting means for saidone channel for removing,A the modulation corresponding in frequency tosaid predetermined frequency from said detected signal output prior toapplication to further translator means.

8. A multiplex system according to claim 6, further comprising aplurality of sources of signals, a plurality of pulse generatorscorresponding in number-to said plurality of trains, means for couplingsaid sources to said pulse generators to signal modulate said pulses,and filter means in said coupling means to block from said signals,frequencies of said predetermined frequency before modulation.

9. A multiplex system according to claim 6, further comprising a,plurality of sources of signals, a.v plurality of pulse generatorscorrespondchannels represented by separate trains of pulses of a givenaverage cadence frequency, interleaved in time with respect to oneanother are transmitted to a receiver circuit in which the separatechannels are selected and segregated and applied to separate receivers,the method of selecting said channels for proper aligned reception,which comprises modulating one of said channels with a synchronizingsignal, selecting said channels in rotation with a selecting periodlonger than the period of said cadence frequency, whereby progressivelydifferent channels will be selected, detecting said selected channels,ltering out said synchronized signal at one of said receivers, andcontrolling said selecting period in response to' said filteredsynchronizing signal to make it correspond to said average cadencefrequency, whereby upon selection of said one channel at said onereceiver, said progressive selection of channels is halted.

6. A multiplex system comprising a first terminal, means fortransmitting a plurality of trains of pulses of a given average cadenceeach train representing a channel of communication,

means for timing said separate trains of pulses' in a given timedisplacement so that the pulses of successive trains are interleavedwith respect to one another to produce a resultant train having a given`average spacing between adjacent pulses, means for modulating the pulsesof the different trains with intelligence signals, means for impartingto the pulses of one of said channels a modulation of a predeterminedfrequency, asecond terminal for receiving said trains of pulses fordetecting the modulations thereon, separate selector means each forselecting a singlel channel, a selector wave generator operating at acadencelower than said given average ca- .ing in number to saidplurality of trains, means for coupling said sources to said pulsegenerators to signal modulate said pulses, filter means in said couplingmeans to block from said signals, frequencies of said predeterminedfrequency before modulation, means for detecting the signal output fromAeach of said selectors, and means in the output of the detecting meansfor said one channel for removing the modulations corresponding infrequency to said predetermined fr equency from said detected signaloutput at a point beyond said filter rst named.

10. In a communication system in which a. plurality of separate channelsrepresented by separate trains of pulses of a, given average cadencefrequency, interleaved in time with respect to one another aretransmitted to a receiver circuit in which the separate channels areselected and segregated and applied to separate receivers, the method ofselecting one of said channels for reception at a given receivingstation which comprises modulating one of said channels with asynchronizing signal, selecting said channels at said receiving stationin rotation with a selecting period longer than said cadence frequency,whereby progressively different channels will be selected, detectingsaid selected channels, lteringcut said 'synchronizedsignal at saidreceiver station, and controlling said selecting period inresponsetosaid ltered synchronizing signal to make it correspond to said averagecadence frequency, whereby upon selection of said one channel at saidreceiver station, said progressive selecsequence, the different trainsrepresentingdifferent channels, means to eiect intelligence moduasiansYlation oi' the pulses oi respective channels, means to modulate thepulses of one channel carrying signal intelligence modulation with agiven 'tinct signal for synchronizing controlya secondV terminal havingmeans for receiving and syn-f chronizing said respectivechannelledtrains of pulses, comprising means for testing in successionsaid trains of pulses including a device responsive to the energy ofsaid distinctive signal and means under control of said device in thetrain to discontinue the succession of testing,

12. A multiplex transmission system according to claim 11, wherein thetesting means appertains for removing energy corresponding to that ofsaid distinct signal from such channels, thereby rendering said onechannel distinctive for use as a synchronizing channel. f

14. In a receiver system for reception of Va given one of a plurality oftrains of pulses interleaved together in time, the pulses of said one ofthe trains being modulated with a signal distinct from the modulation ofthe .other of said trains;

means for selecting the trains of pulses in succession including adevice responsive to the energy of the distinctive signal, means todetect the signals of eachl train of pulses as they are selected, andmeans under control of said responsive device acting in the presence ofenergy of the distinctive signal in the detected signals to discontinuethe succession of the selecting operation of said selecting means,

15. In a receiver system for reception of the signal intelligencemodulation of a given train of pulses interleaved in time spacedrelation with other trains of pulses, said given train being modulatedwith a synchronizing signal distinct from said signal intelligencemodulation; means for selecting the trains of pulses in successionincluding filter means, means to detect the signals of each train ofpulsesas they are selected, said filter means passing only the energy ofsaid synchronizing signal, means to apply said synchronizing signalenergy to said selecting means to discontinue the succession of theselecting operation thereof, and a second lter means to pass the signalintelligence of said given channel and to block said synchronizingsignal energy.

16. In a receiver system for multiplex reception oi a'plurality oitrains of pulses interleaved together in time, one of said trains ofpulses being modulated with a synchronizing signal distinct from asignal energy of the other trains; separate receiving channels for eachAci? a predetermined number of said trains'fof pulses, means forselecting the trains offpulses in succession, means to detect thesignals of each train of pulses as they are selected, illter meansassociated with one of said receiver channels for passing only theenergy of said synchronizing signal, means to apply said synchronizingsignal energy to said selecting means to discontinue the succession ofthe selecting operation thereof, and means controlled by said selectingmeans for rendering the separate receiving channels receptive to pulsesof said trains in accordance with `presence of said distinctive signalin a testedthe interleaved ti ing of said predetermined numberpf,trains' o \\pulse's`. 17. Inacommuni ltion system, means for producing aplurality o Vtrains of pulses interleaved w together in a givensequence, the dilferenttrains representing diierent channels, separate.means for modulating a characteristic of the pulses/oi each of at leastcertain of said channels according to signal intelligence `for suchchannel, means to modulate the pulses of one of saidvchannels with agiven signal frequency as distinguished from the varying frequencies ofthe intelligence signals of the other channels, thereby rendering saidone channel distinctive for synchronizing purposes, a receiver, means totransmit the in terleaved Vtrains of 'pulses to said receiver, means forselecting the,trains of pulses in succession including a deviceresponsive to the energy of the l distinctive signal, means to detect.the signals of each train of pulses as they are selected, and` meansunder control of said responsive device acting in the presence of energyof said 'distinctive signal in the detected signals to discontinue thesuccession of the selecting operation of said selecting means.

18. In a. -multiplex communication system, means for producing aplurality o! trains o'f pulses interleaved together in a given sequence,

kthe different trains representing diierent channels, separate means formodulating .a characteristic of the. pulses of each of at least certainof said channels according to signalintelligence for such channel, meansto modulate thepulses of one of said channels witha signal frequencyoutside the frequency band of the intelligence signals of the otherchannels, thereby rendering said one channel distinctive for use as asynchronizing channel, a receiving-terminal, means to transmit theinterleaved trains of'pulses to said receiving terminal, said terminalhaving a plurality of receiving channels Vcorresponding to at leastcertain of said trains of pulses, means` for selecting the trains ofpulses in rotation, means to detect the signals of each train of pulsesas they are selected, lter means associated with'A one' of said receiverchannels for passing only the energy of said synchronizing channel,means to apply said synchronizing energy to said selectoperationthereof, and means controlled by said selecting means for rendering eachreceiving channel receptive to pulses of said trains in accordance withthe interleaved timing of saidcertain trains of pulses.

19. In a receiver system for reception of a train of pulses having agiven average cadence, the pulses being modulated with synchronizingsignals; a normally blocked selector circuit, means for producingdeblocking pulses at a cadence lower than said average cadence, todeblock said selector circuit whereby said selector circuit is caused toscan in time, means to demodulate the signals of the pulses selected bysaid selector circuit, and means responsive to the presence of energy ofsaid synchronizingsignals in the demodulated signals to cause, saiddeblocking pulse producing means to produce the deblocking pulses atsaid average cadence.

hals; the method comprising selecting increments of received energy at alower cadence than said average cadence to scan in time until saidincrements coincide substantially with the pulses y :mutuo not.

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